There are proposals of systems configured to determine a human activity status or the like. For example, there is a system configured to attach an apparatus provided with an acceleration sensor to a target person whose activity status is determined and determine whether the target person is in a sleep state or an awake state based on an output of the acceleration sensor.
When a user who is a target person whose activity status is determined wears the apparatus on his/her arm, it is automatically determined whether the user is in a sleep state or an awake state from the output of the acceleration sensor. When such an activity meter of a type wearable on the user's body is attached to the body, it is possible to automatically determine whether the user is in a sleep state or an awake state.
However, the user may remove the activity meter from his/her body. When the user removes the activity meter from, for example, his/her arm and leaves the activity meter unattached, the activity meter is placed in an immobile or still state, resulting in a problem that the activity meter misjudges that the user is in a sleep state.